This invention relates to a novel vinylamine copolymer, a flocculating agent for the treatment of waste water using the vinylamine copolymer and a paper strength increasing agent using the vinylamine copolymer in the paper making industry, as well as a process for producing the vinylamine copolymer. More particularly, the present invention relates to a vinylamine copolymer having structural units represented by the following formulas (I), (II), (III), (IV) and (V): ##STR2## wherein X.sup..crclbar. represents an anion or hydroxyl ion, R represents a hydrogen atom or a methyl group, M.sup..sym. represents a hydrogen ion or a monovalent cation), in which the molar fraction of the structural unit (I) is 5 to 85% by mole, the molar fraction of the structural unit (II) is 2 to 85% by mole, the molar fraction of the structural unit (III) is 5 to 80% by mole, the molar fraction of the structural unit (IV) is 0 to 40% by mole, all of said molar fractions being based on the vinylamine copolymer, and the molar fraction of the structural unit (V) is 0 to 8% by mole which is based on the total content of the structural units (III), (IV) and (V), a flocculating agent for the treatment of waste water and a paper strength increasing agent using the vinylamine copolymer in the papermaking industry, as well as a process for producing the vinylamine copolymer, a flocculating agent using the vinylamine copolymer, a paper strength increasing agent using the vinylamine copolymer and a process for producing the vinylamine copolymer.
The novel vinylamine copolymer according to the present invention exhibits excellent effects in the field of application of cationic polymers such as flocculating agents for use in the treatment of waste water, dehydrating agents for organic sludges, drainage aids, retention aids, paper strength increasing agents, etc. in the papermaking industry.
For the preparation of the polyvinylamine, a method by Hofmann reaction of polyacrylamide and hydrolysis of poly-N-vinylamide has been known. Particularly, the method of hydrolysis of a homopolymer of N-vinylformamide is an excellent method which is capable of synthesizing a polyvinylamine of high molecular weight with high stability. However, the resultant polymer is extremely hydrophilic and has only an insufficient effect in the case of using it as a flocculating agent for dehydration. For providing a polyvinylamine with hydrophobic properties, a method of copolymerizing N-vinylformamide and ethylene and then hydrolyzing the resulting product has been known. However, it was difficult to solve the problem by use of the copolymer of N-vinyl formamide and ethylene, since copolymerizability between N-vinylformamide and ethylene is not favorable and, in addition, it is difficult to obtain a copolymer of high-molecular weight.
The present inventors had previously proposed a method of preparing a flocculating agent with good dehydrating properties by copolymerizing N-vinylamide with acrylonitrile, followed by hydrolysis thereby modifying not less than 10 mol % of nitrile groups into carboxyl groups [refer to Japanese Patent Application Laid Open (KOKAI) No. 59-39399(1984)]. Although the effect was remarkable for N-vinylacetamide copolymer shown in the examples, there has been a problem for N-vinylformamide copolymer in that the dehydrating property is remarkably reduced in the case where not less than 10 mol % of the nitrile groups are modified into carboxyl groups. As a result of a further study, the present inventors had proposed a process for producing a flocculating agent by using a basic hydrolyzate of a copolymer of N-vinylformamide and (metha)acrylonitrile [refer to Japanese Patent Application Laid Open (KOKAI) No. 61-118406(1986)]. However, the proposed hydrolyzate still involves a problem in that most of the nitrile groups are modified into carboxyl groups and, in the case where the content of the nitrile group in the starting copolymer is high, water-insoluble polymer is formed or an amphoteric polymer predominantly containing anionic groups results and accordingly, it had been difficult to reduce the water content in the dehydrated sludges in the case of its use as a flocculating agent for dehydration.
For overcoming the foregoing drawbacks, as a result of the present inventors' further studies, it has been found that a vinylamine copolymer of high-molecular weight having hydrophobic properties is obtained by partially modifying a vinylformamide copolymer under acidic conditions. Such vinylamine copolymer has an excellent flocculating effect in the treatment of waste water and also has an excellent paper strength increasing effect in the papermaking industry. The present invention has been attained based on the above findings.